There are plenty of quick guides out there on the internets that'll show you how to convert a cheap & cheerful webcam into a DIY microscope. Basically all that's required is to screw out the focus lens, flip it, and somehow stick it back on.

My approach was to mangle the case and remove the logic board, and then design and print a little mount to hold the lens and the board together.

It's awkward, but it works. I've included two shots of the pixels from my HTC Hero taken with this microscope, and a picture of the microscope itself.